Thanks for the info,
my08yes. I had a shop do pretty much the same thing. I just told them I wanted an aftermarket sub in my 09 EX sedan and they installed a lower-end Powerbass 12'' Sub/Enclosure and bolted a PB amp to the rear of my enclosure. It takes up about 1/4 my trunkspace. They used a LOC and it sounds decent.
I can control the Bass through my stock HU, too. However, they told me not to turn it above Bass3, or else I risk blowing the sub. That's fine with me because I'm a bass lover and surprisingly I keep my Bass at level "C" aka 0, and most my music sounds fine.
I find that if I turn my Bass above level 2 on my stock HU, the sub just completely overpowers the vocals and every other sound coming from the 4 stock 6.5'' speakers, and everything else sounds muddy if you know what I mean. That's why my bass is usually set at 0 or 1 with my setup.
This makes me want to upgrade my 4 stock midrange speakers though...they are just so muddy and unclear since the aftermarket sub dominates the scene

. I want to keep the stock HU, but I assume I'd still need a new amp(s) to power those new speakers, plus another wiring kit or fuses or something. I don't know anything about audio.